American physicist David M. Lee discovered, with Douglas D. Osheroff and Robert C. Richardson in 1972, that helium-3 (He-3, a light, rare, non-radioactive isotope of helium comprised of two protons and one neutron) becomes a superfluid when it is cooled to near absolute zero. Superfluids have a complete absence of viscosity, and behave very differently than ordinary liquids. If circulated in a closed loop, for example, a superfluid could theoretically flow forever, with no friction. The work of Lee, Osheroff, and Richardson radically altered the scientific understanding of how matter behaves at sub-macroscopic scales, and these three scientists shared the Nobel Prize for Physics in 1996. Lee has also studied magnetic resonance, spin polarized hydrogen gas, superconductivity, ultra-low temperature cryogenics, and atomic hydrogen and nitrogen stabilized by matrix isolation in helium-impurity clusters.